Machine with Abradable Ridges and Method

ABSTRACT

A machine having a fixed part including a portion with a smooth surface is provided. The machine also includes a rotating part configured to rotate relative to the fixed part, the rotating part directly facing the portion of the fixed part, and plural ridges formed on the portion of the fixed part directly facing the rotating part, the plural ridges comprising an abradable material, wherein the abradable material is configured to be inoperable at temperatures above about 1000° C.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a national stage application under 35 U.S.C. §371(c) ofprior-filed, co-pending PCT patent application serial numberPCT/US2010/052232, filed on Oct. 12, 2010, which claims priority toItalian Patent Application Serial No. CO2009A000045, filed on Oct. 30,2009, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the subject matter disclosed herein generally relate tomethods and systems and, more particularly, to mechanisms and techniquesfor producing abradable ridges in a machine having a rotating part and afixed part.

2. Description of the Prior Art

Rotating machines, for example, gas turbines, used today in varioustechnical fields (power systems, petrochemical plants, etc.) have atleast a rotating part (rotor with blades) that rotates with respect to afixed part (shroud). A fluid is typically injected at an input of therotating machine to be accelerated/pressurized and the fluid is thenejected at an outlet of the rotating machine. Thus, a fluid flow isgenerated by the rotating blades. For a good efficiency of the rotatingmachine, a seal between the rotating part and the fixed part is desiredto be achieved so that most of the fluid flow is engaged by the bladesof the rotating part and does not leak over the tips of the blades,which is unwanted leakage.

One way to provide the seal between the rotating part and the fixed partof the rotating machine is to deposit an abradable material on the fixedpart so that the tips of the blades together with the abradable materialform a seal. If the abradable material includes a ceramic, then anabrasive material may be provided on tips of the blades of the rotatingpart to protect the tips when contacting the abradable material to formthe seal. Such a method is described in U.S. Pat. No. 6,457,939, theentire content of which is incorporated here by reference. U.S. Pat. No.6,251,526, the entire content of which is incorporated here byreference, describes profiled abradable ceramic coating systems, inwhich a porous ceramic coating is deposited onto a substrate with aprofiled surface, e.g., a metal grid brazed onto the substrate surface(casing of the gas turbine) to form an abradable profiled surface.Because the blades of the rotor of the turbine may increase their sizedue to thermal expansion during the normal operation of the turbineand/or due to centrifugal effects produced by the high rotational speedsof the rotating part of the turbine during operation, the blades maymove towards the casing and may remove part of the abradable material toachieve a smaller clearance. The differential expansion rate between therotating part and the inner surface of the fixed part results in tips ofthe blades contacting the abradable material to carve grooves in thecoating without contacting the casing itself. Thus, a custom-fitted sealwith minimal leakage is formed in the turbine. However, a problem ofsuch techniques is the grid brazed onto the substrate (casing) of theturbine, which may result in damage to the shroud upon profiling.

U.S. Pat. No. 6,887,528 and U.S. Patent Application Publication No.2005/0003172, both of which are assigned to the assignee of the presentpatent application and the entire contents of which are incorporatedhere by reference, disclose a method for producing a profiled abradablecoating on a casing of a gas turbine without providing a grid on thecasing of the turbine. The abradable material includes a porous ceramicmaterial that is able to withstand temperatures as high as 1500° C. Theabradable layer is formed on the casing by using direct-write technologyor plasma sprayed onto the substrate through a mask or a plasma gun.However, this method uses expensive materials for the plural ridges inorder to withstand the high temperatures inside the gas turbines.

For a better understanding of the background art, the following exampleis discussed with regard to FIGS. 1 and 2. As shown in FIG. 1,traditional methods for improving a clearance between the tips of theblades and the fixed part of the turbine is to machine in the casing 10of the turbine a grid 11 by removing part of the original material ofthe casing 10. Then, a thermal barrier coating (TBC) layer 12 (i.e., ahigh temperature resistant layer for protecting the casing from heatdamage) is formed to not be in direct contact with a surface 14 of thecasing 10. An abradable layer 16 is deposited on layer 12. A blade 18 ofthe rotating part faces the abradable layer 16 and may scrape this layer16. As shown in FIG. 2, the abradable layer 16 and the TBC layer 12 maybe shaped as a ridge 20 having a straight-line shape or ridge 22 havinga zigzag shape. However, these traditional methods for providing a hightemperature resistant seal in the turbines may be disadvantageous ifused in other machines that do not experience a high temperature becausecasing 10 may be damaged when machining the grid 11 and/or may beexpensive as the ceramic abradable material requires exotic components,as for example, yttria-stabilized zirconia.

Accordingly, it would be desirable to provide systems and methods forproviding an abradable material on machines that do not operate in ahigh temperature environment.

BRIEF SUMMARY OF THE INVENTION

According to one exemplary embodiment, there is a machine that includesa fixed part having a portion with a smooth surface; a rotating partconfigured to rotate relative to the fixed part, the rotating partdirectly facing the portion of the fixed part; and plural ridges formedon the portion of the fixed part directly facing the rotating part, theplural ridges being made of an abradable material that is configured tobe inoperable at temperatures above about 1000° C. At least one ridge ofthe plural ridges is curved.

According to another exemplary embodiment, there is a diaphragm of acompressor that includes a fixed part configured to accommodate at leastan impeller of the compressor and having a portion with a smoothsurface; and an abradable layer formed on the portion with the smoothsurface of the fixed part. The abradable layer is machined to formplural ridges directly facing the impeller, the plural ridges'being madeof an abradable material that is configured to be inoperable attemperatures above about 1000° C., and at least one ridge of the pluralridges is continuously curved.

According to still another exemplary embodiment, there is a method ofdepositing an abradable material on a diaphragm of a machine. The methodincludes identifying in the diaphragm a portion with a smooth surfacethat directly faces a rotating part of the machine; depositing anabradable layer on the portion directly facing the rotating part, theabradable layer including an abradable material that is configured to beinoperable at temperatures above about 1000° C.; and machining pluralridges in the abradable layer such that at least one ridge of the pluralridges is curved.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. In thedrawings:

FIG. 1 is a schematic diagram of a portion of a conventional gas turbinewith an abradable material deposited on a grid formed in the casing ofthe gas turbine;

FIG. 2 is a schematic diagram of a conventional pattern of the abradablematerial of FIG. 1;

FIG. 3 is a schematic diagram of a compressor;

FIG. 4 is a schematic diagram of an impeller of the compressor of FIG.3;

FIG. 5 is a schematic diagram of a portion of a diaphragm of acompressor according to an exemplary embodiment of the presentinvention;

FIG. 6 is a schematic diagram of an abradable material deposited on adiaphragm of a compressor according to an exemplary embodiment of thepresent invention;

FIG. 7 is a schematic diagram of a pattern of plural ridges formed in anabradable material according to an exemplary embodiment of the presentinvention;

FIG. 8 is a schematic diagram of various ridge shapes that can be formedaccording to an exemplary embodiment of the present invention;

FIG. 9 is a schematic diagram of an interaction between ridges and animpeller of a compressor according to an exemplary embodiment of thepresent invention;

FIG. 10 is a schematic diagram of various layers that may be formed on adiaphragm of a compressor according to an exemplary embodiment of thepresent invention;

FIG. 11 is a graph showing advantages of curved patterns for the ridgesformed on a diaphragm according to an exemplary embodiment of thepresent invention; and

FIG. 12 is a flow chart illustrating steps for forming the plural ridgeson the diaphragm of a machine according to an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the exemplary embodiments refers to theaccompanying drawings. The same reference numbers in different drawingsidentify the same or similar elements. The following detaileddescription does not limit the invention. Instead, the scope of thepresent invention is defined by the appended claims. The followingembodiments are discussed, for simplicity, with regard to theterminology and structure of a compressor. However, the embodiments tobe discussed next are not limited to compressors, but may be applied toother systems that require a seal between a rotating part and a fixedpart.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the subject matter disclosed. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout the specification is not necessarily referringto the same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

FIG. 3 illustrates an open impeller centrifugal compressor 30. The openimpeller centrifugal compressor 30 has an impeller 32 connected to ashaft 34. Shaft 34 may be supported by bearings 36 and 38. The impeller32 has a hub portion 40 and a blade portion 42. A fluid enters thecentrifugal compressor 30 at an inlet 44, along an incoming direction A.The fluid reaches the impeller 32, where it is accelerated based on thecentrifugal force while changing the fluid direction prior to beingdischarged at outlet 46 along direction B. A diaphragm 48, which facesthe impeller 32, is part of the fixed part of the compressor 30. Thediaphragm may be attached to a casing 49 of the compressor 30.

A detailed view of the impeller 32 is shown in FIG. 4. Other structuresfor the impeller 32 may be used. The specific shape of impeller 32 shownin FIG. 4 corresponds to an open impeller (no element is covering bladeportion 42). A centrifugal compressor having this impeller is called anopen impeller centrifugal compressor. The blade portion 42 may havemultiple blades 50 having various contours, depending on theapplication/operation of the compressor. These multiple blades 50 rotateinside the diaphragm 48 such that tips 52 of the blades 50 may movecloser or even touch the diaphragm 48 due to an elongation of the blades50 because of thermal transients, and/or the high rotational speed ofthe blades 50 relative to the diaphragm 48, and/or critical vibrations.

To prevent damages to the tips 52 of the blades 50 and also to achieve adesirable seal between blade tips 52 and diaphragm 48, as has beendiscussed in the Background of the Invention section, an abrasivematerial may be coated on tips 52. However, no such abrasive material isused in this exemplary embodiment. Thus, tips 52 of the blades 50 arevulnerable to damage if they contact the strong material that thediaphragm 48 is made. For this reason, a continuous layer of abradablematerial is deposited on a portion of the diaphragm 48 that directlyfaces blades 50. This portion is shown in FIG. 5 as element 60.According to another exemplary embodiment, portion 60 may be smallerthan shown in FIG. 5, i.e., may not extend the entire axial span of theblade portion 42. According to this exemplary embodiment, portion 60 maybe one third of the axial span of the blade portion 42. In other words,considering axis X as being parallel to the rotation axis of impeller32, the axial span of the blade portion 42 is between C and F. The axialspan of portion 60, which has the abradable material thereon, may bebetween C and F or smaller, with the smallest axial span being between Eand F.

Another feature of the novel exemplary embodiments is that the diaphragm48, and more specifically, a surface 62 (see FIG. 5) of the diaphragm 48that receives the abradable material is smooth, i.e., has no ridges,grids, or other formations intentionally formed in the metal of thediaphragm 48. In one application, the surface 62 of the portion 60 ofthe diaphragm 48, if represented in a XY plane, with a longitudinal axisof the diaphragm 48 along axis X, has a same sign of a partialderivative of a Y position with respect to X along the longitudinal axisof the diaphragm 48 ignoring normal tolerances accepted in the industryfor making such large pieces of equipment. Further, even if smallunevennesses are present in the surface 62 of portion 60, if these arenot intentionally made, it is considered that the surface 62 is smooth.This is different from some gas turbine shrouds that have ridges orgrids 11 intentionally formed in the casing 10 of the gas turbine priorto depositing the abradable material 16, as shown in FIG. 1.

Another difference between the traditional gas turbines and the novelembodiments is the temperature range. More specifically, the gasturbines are known to operate at high temperatures, e.g., higher thanabout 1000° C., while a compressor operates at lower temperatures, inthe range from about 100 to about 400° C., and about 200° C. for acentrifugal compressor diaphragm. This large difference in the operationtemperature of a gas turbine and a compressor makes the ceramic basedabradable coatings of the traditional turbines not suitable/unnecessaryfor compressors. Thus, other materials, as will be discussed later, areused for coating the diaphragm of the compressors.

According to an exemplary embodiment illustrated in FIG. 6, the surface62 of the diaphragm 48 may be directly covered with a smooth layer 70 ofan abradable material. The layer 70 of abradable material may bedirectly deposited on the surface 62 of the diaphragm 48, which isdifferent from the gas turbine case in which the TBC layer is formed onthe casing prior to depositing the abradable material. The directformation of the abradable material 70 on the surface 62 of diaphragm 48is possible because of the lower temperature environment in whichcompressors operate.

Abradable materials to be used for compressors may be divided intometallic-based abradable materials and plastic-based abradablematerials. These materials have a common property that they are notdesigned to withstand high temperatures, as those materials used in agas turbine. In other words, the abradable materials to be used in thecompressors may become inoperable (melt, peel, etc.) if used in theturbine of a gas turbine. In this regard, the abradable materials to beused, for example, in centrifugal compressors, are selected to operateat temperatures up to about 200° C. In another embodiment, depending onthe type of compressor, the abradable materials may operate attemperatures up to about 400° C. Metallic abradable materials mayinclude one or more of AlSi, AlSi and Polyester, NiCrFeBNAl, etc.Plastic abradable materials may include one or more ofpolytetrafluoroethylene (PTFE), Polyester, polyimide, etc.

It is noted that the metallic and/or plastic abradable material may beformed directly on the surface of the diaphragm 48, without anyprotection layers (for example, TBC layers) as is customary in the gasturbines. In this regard, a known ceramic abradable material is notdirectly deposited on the substrate but rather on a thermally resistantcoating (layer 12 in FIG. 1), for protecting the substrate (the casing)from the high temperatures generated during the operation of the gasturbines. In another exemplary embodiment, such thermally protectivecoatings may be deposited on the diaphragm 48 prior to depositing theabradable material 70.

After the abradable material 70 has been deposited on the surface 62 ofthe diaphragm 48, the abradable material 70 may be machined to formridges 72 having peaks 74 and valleys 76 as shown in FIG. 7. The shapeof the ridges 72 may be diamond shape, straight lines, constantlycurved, continuously curved, etc. A cross sectional view of ridges 72 isshown in FIG. 8. A shape of ridge 72, as shown in the cross sectionalview in FIG. 8, may have a smooth shape as indicated by 80, or may havea triangular cross section as indicated by 82, or may have a rectangularcross section as indicated by 84, or other shapes. According to anexemplary embodiment, the diaphragm 48 may be provided with acombination of one or more of the above discussed shapes 80, 82, and 84.For exemplary purposes, a dimension “d” of the ridges 72 may be betweenabout 0.0025 and about 0.102 mm for the rectangular shape and betweenabout 0 and about 0.102 mm for the triangular shape, and a height “h” ofthe ridges 72 may be between about 0.1 and about 0.5 mm.

Once blades 50 are rotating with shaft 34 inside diaphragm 48, due tocentrifugal effects and/or rotor unbalance and/or thermal transients,the blades may move radially or axially towards the diaphragm 48 tocontact ridges 72. Depending on the degree of expansion of the blades50, tips 52 of the blades 50 may touch and even break (remove) top partsof ridges 72 to form groove regions 90 as shown in FIG. 9. This closecontact between ridges 72 and blades 50 may achieve the desired sealingbetween the rotating part and the fixed part of the compressor. Inaddition, the close contact of the tips 52 of the blades 50 with ridges72, which are abradable and also have a soft structure due to theirsmall physical dimensions, prevents the tips 52 of the blades 50 tosuffer damages, given the fact that tips 52 have no protective abrasivematerials. In addition, if a thickness of the ridge 72 is small, thematerial used to form the ridge may be dense.

According to another exemplary embodiment, the entire diaphragm 48 maybe made of the abradable material so that the ridges 72 may be formed bymachining the diaphragm 48 and not by depositing abradable material.

A more detailed view of the layers deposited on the surface 62 of thediaphragm 48 according to an exemplary embodiment is shown in FIG. 10. Abond coat layer 100 (for example, the bond coat can be NiAl or NiCrAlY)having a height h1 of around 0.125 mm optionally may be deposited on thediaphragm 48 by, for example, plasma spray process. Optionally, a layer102 of DVC-TBC (Dense Vertically Cracked Thermal Barrier Coating) havinga height h2 of about 1.00 mm may be deposited over layer 100. Theabradable layer 70 is formed over layer 102 or directly on layer 100 ordirectly on diaphragm 48 and may have a height h3 of about 1.3 mm.Deviations from these exemplary numbers in the range of 5% to 50% arealso possible.

Advantages of the novel abradable patterns discussed above are nowdiscussed with regard to FIG. 11. FIG. 11 shows the variation of a totalclearance reduction as a function of hot running rubbed clearance forvarious abradable ridge shapes having the same height. The hot runningrubbed clearance is the actual clearance between the impeller and thediaphragm when the impeller rotates and the total clearance is theeffective clearance due to the shape of the ridges and other parameters.FIG. 11 illustrates the relative effect of (i) abradable ridges with acurved pattern (curve 124), (ii) abradable ridges with 45 degreesstraight line pattern (curve 122), and (iii) a smooth abradable layerwith no ridges and no pattern (curve 120). For a given hot clearance(e.g., 102 mils, location 126 in FIG. 11), the abradable ridges withcurved pattern provide an advantage of approximately 18 mils clearancereduction over the plural ridges with the straight line pattern. Thecurved pattern may provide approximately 40 mils clearance reductionover a compressor with no abradable layer versus approximately 27 milsclearance for the straight line pattern over the no abradable layercompressor. Curve 122 corresponds to plural ridges having a straightpattern inclined at 45 degrees relative to the axial direction of thecompressor (see for example FIG. 2, ridges 22) and curve 124 correspondsto plural ridges having curved patterns (see for example FIG. 7, ridges72). It is noted that the curved patterns curve 124 provides a higherclearance reduction (approximately 40 mils or 1 mm) than the straightpattern curve 122 (clearance reduction approximately 27 mils or 0.68 mm)and the smooth abradable layer curve 120 (approximately 23 mils or 0.58mm) for the same hot running rubbed clearance 126. The total clearancereduction shown on the Y axis of FIG. 11 indicates that for a sameheight of the ridges 72 of the three curves 120, 122, and 124, theamount of fluid leaked between the moving part and the fixed part of thecompressor is smaller for ridges 72 of curve 124 than for ridges 72 ofcurve 122. The shape of the ridges (straight versus curved) generatethis effect of reduced clearance.

According to an exemplary embodiment, which is illustrated in FIG. 12,there is a method for depositing an abradable material on a diaphragm ofa machine. The method includes a step 130 of identifying in thediaphragm a portion with a smooth surface that directly faces a rotatingpart of the machine; a step 132 of depositing an abradable layer on theportion directly facing the rotating part, the abradable layer includingan abradable material that is configured to be inoperable attemperatures above about 1000° C.; and a step 134 of machining pluralridges in the abradable layer such that at least one ridge of the pluralridges is curved.

The disclosed exemplary embodiments provide a system and a method fordepositing an abradable material on a fixed part of a machine having amoving part. However, the exemplary embodiments are intended to coveralternatives, modifications and equivalents, which are included in thespirit and scope of the invention as defined by the appended claims.Further, in the detailed description of the exemplary embodiments,numerous specific details are set forth in order to provide acomprehensive understanding of the claimed invention. However, oneskilled in the art would understand that various embodiments may bepracticed without such specific details.

Although the features and elements of the present exemplary embodimentsare described in the embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the embodiments or in various combinations with or withoutother features and elements disclosed herein.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other example are intended to be within the scope of theclaims.

1. A machine comprising: a fixed part comprising a portion with a smoothsurface; a rotating part configured to rotate relative to the fixedpart, the rotating part directly facing the portion of the fixed part;and plural ridges formed on the portion of the fixed part directlyfacing the rotating part, the plural ridges comprising an abradablematerial, wherein the abradable material is configured to be inoperableat temperatures above about 1000° C., wherein at least one ridge of theplural ridges is curved.
 2. The machine of claim 1, wherein the entireof at least one ridge of the plural ridges is continuously curved. 3.The machine of claim 1, wherein all of the plural ridges arecontinuously curved.
 4. The machine of claim 1, wherein the pluralridges are configured to be inoperable at temperatures above about 400°C.
 5. The machine of claim 1, wherein the abradable material is plasticor metal based.
 6. The machine of claim 5, wherein the plastic abradablematerial comprises one or more of polytetrafluoroethylene (PTFE),polyimide or Polyester.
 7. The machine of claim 5, wherein the metallicabradable material comprises one or more of AlSi, AlSi and Polyester, orNiCrFeBNAl.
 8. The machine of claim 1, wherein the abradable materialcovers a region of the portion of the fixed part that spans one third orless of an axial span of the rotating part.
 9. The machine of claim 1,further comprising: a diaphragm configured to enclose the rotating part,wherein the entire diaphragm is made of the abradable material.
 10. Themachine of claim 1, wherein a cross section of at least one ridge of theplural ridges is a rectangle or a triangle.
 11. The machine of claim 10,wherein a height of the rectangular or triangular ridges is betweenabout 0.1 to about 0.5 mm.
 12. The machine of claim 1, wherein therotating part further comprises: plural blades disposed on the rotatingpart, wherein tips of the plural blades are configured to touch one ormore of the plural ridges when the rotating part rotates and wherein thetips of the plural blades are not treated to include the abrasivematerial.
 13. The machine of claim 1, wherein the machine is an openshroud centrifugal compressor and an operating temperature of thecentrifugal compressor is less than about 200° C.
 14. A diaphragm of acompressor, the diaphragm comprising: a fixed part configured toaccommodate at least an impeller of the compressor and comprising aportion with a smooth surface; and an abradable layer formed on theportion with the smooth surface of the fixed part, wherein the abradablelayer is machined to form plural ridges directly facing the impeller,the plural ridges comprising an abradable material, wherein theabradable material is configured to be inoperable at temperatures aboveabout 1000° C., and wherein at least one ridge of the plural ridges iscontinuously curved.
 15. The diaphragm of claim 14, wherein theabradable material is plastic or metal based.
 17. The diaphragm of claim15, wherein the plastic abradable material comprises one or more ofpolytetrafluoroethylene (PTFE), polyimide, or Polyester and the metallicabradable material comprises one or more of AlSi, AlSi and Polyester, orNiCrFeBNAl.
 18. A method of depositing an abradable material on adiaphragm of a machine, the method comprising: identifying in thediaphragm a portion with a smooth surface that directly faces a rotatingpart of the machine; depositing an abradable layer on the portiondirectly facing the rotating part, the abradable layer comprising anabradable material, wherein the abradable material is configured to beinoperable at temperatures above about 1000° C.; and machining pluralridges in the abradable layer such that at least one ridge of the pluralridges is curved.
 19. The method of claim 18, further comprising:machining all of the plural ridges to be continuously curved.
 20. Themethod of claim 18, further comprising: preparing the abradable materialto be plastic or metal based, wherein the plastic abradable materialcomprises one or more of polytetrafluoroethylene (PTFE), polyimide, orPolyester and the metallic abradable material includes one or more ofAlSi, AlSi and Polyester, or NiCrFeBNAl.